One technology for after-treatment of engine exhaust utilizes selective catalytic reduction (SCR) to enable certain chemical reactions to occur between NOx in the exhaust and ammonia (NH3). NH3 is introduced into an engine exhaust system upstream of an SCR catalyst by injecting urea into an exhaust pathway. The urea entropically decomposes to NH3 under high temperature conditions. The SCR facilitates the reaction between NH3 and NOx to convert NOx into nitrogen (N2) and water (H2O). However, issues may arise upon injecting urea into the exhaust pathway. In one example, urea may be poorly nixed into the exhaust flow (e.g., a first portion of exhaust flow has a higher concentration of urea than a second portion of exhaust flow) which may lead to poor coating of the SCR and poor reactivity between emissions (e.g., NOx) and the SCR.
Attempts to address poor mixing include introducing a mixing device downstream of a urea injector and upstream of the SCR such that the exhaust flow may be homogenous. One example approach is shown by Collinot et al. in U.S. 20110036082. Therein, an exhaust mixer is introduced to an exhaust pathway to both reduce exhaust backpressure as exhaust flows though the mixer and increase exhaust homogeneity. The exhaust mixer comprises one or more helicoids which may manipulate an exhaust flow to flow within an angular range of 0 to 30°.
However, the inventors herein have recognized potential issues with such systems. As one example, the mixer introduced by Collinot has a relatively long body and may additionally comprise one or more mixer bodies adjacent to one another. The mixer bodies may vibrate and collide with one another, due to either road conditions or turbulent exhaust flow, which may produce undesired audible sounds and/or prematurely degrade the mixer.
In one example, the issues described above may be addressed by an exhaust gas mixer comprising a most upstream first section, followed consecutively by second, third, and fourth sections. The first and third sections each have a plurality of teardrop-shaped projections. The second and fourth sections each have a plurality of teardrop-shaped projections radially misaligned with the projections of the first and third sections. In this way, it is possible to achieve improved mixing by taking advantage of more normal/binomial distribution of flow that presents numerous points at which the flow can take different paths, similar to a Galton box or quincunx device.
As one example, a mixer with consecutive first, second, third, and fourth sections may be used to increase a homogeneity of an exhaust gas. The portions may be complementary to one another such that an exhaust flow is altered as it passes through each portion of the mixer. The first, second, third, and fourth sections may be physically coupled to a mixer pipe, but not physically coupled to one another. In this way, the mixer can be compact, which may increases mixer stability along with allowing the mixer to be placed in a greater number of locations. Additionally, due to its compact nature, the mixer may produce lower audible sounds due to exhaust turbulence.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.